Air cycle machines (ACM) are used in many aircraft environmental control systems (ECS). The ECS, as is generally known, is used to manage cooling, heating, and pressurization of the aircraft. The ACM typically takes the form of a compact, rotary compressor based system, and may include a compressor, a heat exchanger, a fan, a turbine with blades and bearings, such as journal bearings, and a shaft connecting the compressor, fan and turbine. The ACM compressor receives compressed ambient air from an engine compressor or auxiliary power unit, further compresses the air, and supplies the further compressed air to the ACM turbine. The further compressed air expands through the ACM turbine, providing power as well as a cool, fresh air supply for the aircraft.
ACMs, like many apparatus, are susceptible to wear, and are a relatively expensive ECS part to repair and overhaul. One source of wear for ACMs results from ice formation and shedding on ACM turbine blades. This ice formation and shedding on the ACM turbine blades can result in imbalance conditions for the ACM turbine blades, causing wear to ACM journal bearings. The ice formation and shedding, and resulting ACM bearing wear, is difficult to accurately predict due to dynamic conditions in the ACM, and such ACM wear is generally not detected until after the wear has become significant enough so as to have noticeable deleterious effects on the ACM. Once these noticeable deleterious effects have occurred, the ACM can become much more expensive to repair.
Accordingly, there is a need for a method and apparatus to accurately predict ice formation and shedding, and resulting ACM wear, under dynamic conditions associated with an ACM.